Exemplary embodiments herein relate to an idle stop control system and method for a vehicle.
In view of high fuel prices and ever more stringent regulations relating to improved fuel economy and vehicle emissions, vehicle manufacturers are applying idle stop (or start-stop) technology to vehicles equipped with conventional internal combustion engines (e.g., vehicles that are not hybrid-electric or HEVs). However, one concern area for vehicles equipped with idle stop technology is how to maintain comfort within the cabin of the vehicle while the engine is turned off during an idle stop. The current industry accepted method of heating the cabin after the engine is turned off at a stop for non-HEVs is to continue to circulate engine coolant with an auxiliary electric water pump. Another option for maintaining heat within the vehicle cabin is to replace the conventional mechanical water pump with an electric pump so that no auxiliary pump is needed. In either case, residual engine heat can be transported to the heater core, which warms air from the HVAC blower fan to maintain heat within the vehicle cabin.
There are several drawbacks with these options. For example, idle stop technology can be expensive and adding an auxiliary electric water pump or a standalone replacement electric water pump only adds to this cost. Also, once the engine is off during an idle stop, there are concerns related to maintaining the charge of the vehicle's primary battery. Running an electric water pump along with the blower fan only adds to the high electrical load on today's feature rich vehicles during an idle stop. Running the electric water pump while the engine is off may further limit the amount of time before the battery is not able to restart the engine.
Additionally, utilizing an auxiliary pump requires added weight and packaging space, both of which are negatives from a vehicle design standpoint. Finally, the electric water pump typically provides far more performance than is necessary for the average stop time (e.g., in the United States) at a stop sign, traffic signal, random stop in heavy traffic, etc. In the US, stop times can range anywhere from a few seconds to several minutes in traffic or even hours depending on conditions. The electric water pump would only be necessary for extended engine off time periods, which probably cannot be permitted due to concerns with battery charge and engine temperature. In terms of performance, the electric water pump only has a significant advantage in extremely cold conditions. Such conditions are not typically experienced by most vehicle drivers within the United States. In warmer conditions, assuming the vehicle's cabin is allowed to fully saturate to a comfortable temperature first, the sole use of the HVAC blower fan to heat the cabin using only residual heat in the heater core and in the vehicle's cabin air provides more than adequate comfort for short engine stops.